This invention relates to quiet bouncer drive method and apparatus in which a massive piston weight is bounced upon a cushion of compressed gas trapped between the piston weight and a bottom assembly, whereby physical contact between the piston weight and bottom assebmly is avoided. More particularly, this invention relates to such pile driver method and apparatus wherein the feeding of compressed gas into the bounce chamber between the piston weight and the bottom assembly is automatically controlled by movement of the piston weight.
Conventional pile drivers of the diesel or steam type use a falling weight or hammer to strike down upon an anvil surface to transmit a blow to a pile. The forces on the anvil resulting from such a noisy, striking type blow become destructive when the energy levels needed to drive a pile become high. In my U.S. Pat. No. 3,714,789, entitled "Automatically Self-Regulating Variable Stroke Variable Rate and Quiet Operating Pile Driver Method and System", I describe a pile driver that overcomes the above and other disadvantages inherent in the conventional steam type or diesel type pile drivers, and this new type of pile driver, which is quiet operating may be called a "bouncer" pile driver; it has a massive piston weight that is advantageously bounced upon a cushion of pressurized gas during operation.
Such a quiet-operating "bouncer" pile driver is also described in U.S. Pat. Nos. 3,788,402 and 3,721,095 in my name as inventor. In the latter patent, there are described advantageous methods and systems for determining the magnitude of the driving forces being exerted on the pile during each powerful bouncing stroke and for controlling the force of the pile driving thrusts as may be desired to enhance the pile-driving operation. The reader may wish to review these patents as background information about the relatively new technology of quiet-operating bouncer pile drivers.
In the bouncer pile driver described in the above-mentioned patents, pressurized gas stored in a bottom assembly is valved into a bounce chamber located between the piston weight and the bottom assembly. This valving occurs during each bounce cycle when the descending piston weight contracts against a plunger head of a valve protruding upwardly from the top of the bottom assembly. Such contacting engagement between the moving piston weight and the initially stationary plunger head of the valve causes rapid acceleration of the valve with consequent stressing of the valve parts.